Astronauts upgrading the Hubble Space Telescope have made a third spacewalk in as many days to make repairs deep inside the orbiting observatory.
Mission chief mechanic John Grunsfeld delved into the interior of Hubble to replace computer circuitry that was never meant to be repaired in space.
He was joined by Andrew Feustel to install a new $88m (£58m) spectrograph.
The instrument will provide greater insight into how planets, stars and galaxies are formed.
This footage shows the spectorograph being fitted.